The first time I replaced the washers, I put them on backwards. On hardtopguy.com he has a pic of "Differential Drain & Fill Plug Washers" yet in the pic, the copper washer is pictured first which would lead one to believe it is for the drain plug. This is incorrect of course, but I didn't have any problem. In fact I ran NO washer on the drain bolt for 10k miles without a problem. I even undertorqued it a bit to make sure I wasn't harming the threads.